By "Boss run-up" I am specifically referring to the act of having to run through several parts of a level to a boss after dying instead of simply having a checkpoint at the boss battle.
I'm not quite sure how far back this trend dates, but the first real time I remember experiencing it was in Demons Souls and subsequently all the later entries. Currently I'm playing Hollow Knight and it also features this mechanic. There are benches where you sit and save your progress/respawn, and then all the boss fights are located several screens away. I thankfully haven't died all that many times to the bosses, but one encounter with a "sub boss" took me around 10 tries or so and I kept getting aggravated a lot more by having to traverse the same set of rooms just to get to the fight than the actual fight itself (which was also kind of annoying). The more I think about it the more I don't really see any reason for this design choice. What is it supposed to accomplish? I suppose if you could just restart right at the boss or boss-door each time it would take a lot faster to figure out the moveset and move on. But is that it? Is the entire purpose just to prolong the game time because you're pulled out of your rhythm and have to run back to the boss?
A lot of modern design choices I get and I'm happy with but this one I just don't like. As an adult whose game-playing time is systematically shrinking due to "life" any part of a game that makes me waste time is a nuisance.